Field of the Invention
The invention relates in general to gas testing devices and in particular to a new and useful test vial for the detection of gas components in the air, with a packing that varies along the longitudinal axis of the test vial.
Such test vials have become known from the U.S. Pat. No. 3,620,677. There, a granular packing impregnated with a color reagent is contained in an envelope that changes shape along its lateral axis. With this the progression of the zone of reaction needed for the detection of a gaseous hazardous substance can be calibrated by suitable selection of the packing cross section and its change along the longitudinal axis of the test vial in such a manner that, at different gas concentrations, the discolored area has a definite specific relation to the amount of the detected hazardous substance. A test vial which shall permit the desired accuracy of measurement even in different measuring ranges of the test vial, can be produced by giving the packing a suitable shape.
Since the known test vials have different cross sections of the area, with impregnated packing material, through which the stream of gas containing the hazardous substance is flowing and which are arranged in succession along the axis of the test vial, the gas to be analyzed will have various flow rates and profiles. This irregular flow, due to the not entirely uniform packing of the carrier material, results in locally different air resistances. Because of the changing flow rates there is no guarantee that the necessary time of direct contact of the hazardous substance to be detected with the impregnated packing is maintained in all parts within the test vial to bring about a quantitative reaction of the indicator. The desired accuracy of measurement is thereby destroyed again.